1. Field of the Invention
The invention relates to an exhaust system. The exhaust system is provided, for example, for a car but may also be used for another motor vehicle--for example a truck or bus The internal combustion engine may consist of a gasoline or diesel engine.
When a motor vehicle is used, the internal combustion engine generates vibrations, i.e. oscillations, of the engine casing. Furthermore, rapid changes in the power output by the engine can cause swivel movements of the engine casing about a virtual axis of rotation and/or pivot axis. The oscillatory movements and other movements of the engine casing are transmitted to the exhaust via the mechanical link between said casing and said exhaust. Moreover, the engine feeds exhaust gas to the exhaust in a pulsating manner, which exhaust gas can also generate oscillations of the exhaust. Furthermore, driving over holes and other irregularities, driving around curves and the acceleration and braking of the vehicle cause accelerations of the exhaust. The exhaust is furthermore heated by the exhaust gas during operation of the engine, the exhaust gas temperature decreasing in a direction away from the engine, along the flow path. Owing to the thermal expansion of the rigid parts of the exhaust, the heating results in a temporary lengthening of said exhaust.
2. Description of the Prior Art
An exhaust system disclosed in German Patent Application Publication 31 37 746 has an exhaust which has in succession, in the direction of flow of the exhaust gas, a pipe, a deformable pipe member, a first silencer, a deformable pipe member, a pipe, a second silencer and a pipe. Each silencer has a casing. The exhaust is held on the vehicle body by retaining means. The retaining means have suspension means with rubber rings, said suspension means engaging the pipes. Similar exhaust systems having rubber rings are also known in practice. If a force is exerted on an exhaust part held by means of rubber rings, the rubber rings first offer only a very small resistance to a deflection of the retained exhaust part from its rest position. Only when the deflections of the exhaust parts reach certain limits, which are generally 1 to 2 cm or more in practice, does the resistance generated by the rubber rings increase abruptly. The parts held by the retaining means can thus move almost freely within the ranges defined by the stated limits.
The deformable pipe members are intended to decouple silencers arranged downstream of said members and other exhaust parts from the engine with respect to vibration. Since the known exhausts and in particular their parts arranged downstream of the deformable pipe members can move fairly freely within certain limits, transverse oscillations of large amplitudes are frequently generated in the exhausts. This is the case in particular when the exhausts have resonant frequencies in the region of the fundamental oscillations generated by the engine. The oscillations and other accelerations and forces acting on the exhaust subject the pipes belonging to the exhaust, silencer casings and deformable pipe members to considerable stress. The pipes and casings of the known exhausts have thick walls. The known exhaust systems are therefore heavy. The high weight of the known exhaust systems requires a great deal of material for their manufacture, for example relatively expensive stainless steel, and in particular increases the fuel consumption during driving. Furthermore, in spite of the large wall thicknesses, the exhausts fracture fairly frequently. Since the silencers of the known exhausts are usually deflected transversely with respect to the general longitudinal direction of the exhausts, starting from their middle and/or rest position, in various transverse directions up to at least 1 cm and often up to 2 cm or more, they also require space for their transverse movements in addition to the space occupied by them. This often has the disadvantage that the silencer cannot be made as large as desirable for good silencing.
European Patent Application Publication 0 807 749 published on Nov. 19, 1997, and the corresponding U.S. patent application Ser. No. 08/853,183 (1997) proposed exhausts which have two deformable pipe members connected by a rigid pipe and two or three catalytic converter and/or silencer casings arranged downstream thereof. Furthermore, retaining means were provided for holding each of these casings relatively firmly on the vehicle in such a way that each of these casings is at most slightly displaceable in all directions and in particular in the longitudinal direction of the vehicle and hence in the general longitudinal direction of the exhaust. These retaining means make it possible considerably to reduce oscillations and other movements of the casings and of the entire exhaust and to make said exhaust thin-walled, light and nevertheless durable. However, the exhaust systems according to this proposal also have the disadvantage that expensive, deformable pipe members must be arranged between the stated, successive casings in order to compensate the changes in length which are caused during operation by the thermal expansions of rigid exhaust parts.